The present invention relates to a paper feed unit, and more particularly, to a paper feed unit for further feeding a sheet from the position at which the tip end of the sheet contacts with a secondary paper feed member by a primary paper feed roller to complete primary paper feed in a state in which the sheet is being bent.
FIG. 7 is schematic structural diagram of a conventional paper feed unit A1.
In FIG. 7, many print sheets (or sheets) 2 are stacked on the paper feed tray 1 of the paper feed unit A1. A scraper roller 3 and a pickup roller 4, which are primary paper feed rollers, are located above the stacked print sheets 2. The scraper roller 3 press-contacts with the uppermost print sheet 2 and the pickup roller 4 press-contacts with a stripper tray 5.
The rotary shaft 6 of the pickup roller 4 and the rotary shaft 7 of the scraper roller 3 are coupled to each other by a driving belt V. The pickup roller 4 and the scraper roller 3 are rotated in paper feed rotation direction synchronously with each other by the rotation of the rotary shaft 6 of the pickup roller 4.
A pair of secondary paper feed rollers 8 and 9 are arranged to press-contact with each other on the transfer downstream side of the pickup roller 4. The paired secondary paper feed rollers 8 and 9 are driven to rotate in opposite rotation directions so as to transfer the print sheet 2 put between the rollers 8 and 9.
Also, a paper feed sensor 10 is provided between the pickup roller 4 and the paired secondary paper feed rollers 8 and 9. The paper feed sensor 10 detects the tip end of the print sheet 2 transferred from a primary paper feed side.
Description will be given to the paper feed operation of the paper feed unit constituted as stated above.
When the scraper roller 3 and the pickup roller 4 rotate synchronously with each other, at least the uppermost print sheet 2 press-contacted with the scraper roller 3 is transferred and then the transferred print sheet 2 is transferred to the position between the pickup roller 4 and the stripper tray 5.
Since the print sheet 2 which has been transferred to the position between the pickup roller 4 and the stripper tray 5 is press-contacted with the pickup roller 4, the sheet 2 is transferred further in response to the rotation of the pickup roller 4.
If it is assumed that a plurality of print sheets 2 are transferred to the position between the pickup roller 4 and the stripper tray 5, the uppermost print sheet 2 is applied with a transfer force by the rotation of the pickup roller 4 and the lowermost print sheet 2 is applied with a transfer resistance by the stripper tray 5, whereby only the uppermost print sheet 2 is transferred to the paired secondary paper feed rollers 8 and 9 side.
When the paper feed sensor 10 detects the tip end of the print sheet 2 transferred, the rotation of the scraper roller 3 and that of the pickup roller 4 are stopped at the point at which the print sheet 2 has been transferred by a predetermined distance with reference to this detection point. To be specific, the print sheet 2 is contacted with the paired secondary paper feed rollers 8 and 9 while the tip end thereof is put between the paired secondary paper feed rollers 8 and 9, and transferred further from this contact position. Then, primary paper feed is completed while the print sheet 2 is being bent as shown in FIG. 7.
If the primary paper feed is completed while the print sheet 2 is being bent as stated above and the paired secondary paper feed rollers 8 and 9 are driven to rotate, then the print sheet 2 is put between the paired secondary paper feed rollers 8 and 9 smoothly and surely by the returning force of the bent print sheet 2 for returning to a linear state while eliminating the inclination of the sheet caused by the oblique feed of the sheet during the transfer process. It is, therefore, possible to perform secondary paper feed at accurate, surely timing.
However, due to the further studies done by the inventors of the present invention, if the primary paper feed is completed in a state in which the print sheet 2 is being bent as shown in FIG. 7, the pickup roller 4 may be possibly rotated in counter direction by the returning force of the bent paper sheet 2 for returning to a linear state and the rear end of the paper sheet 2 moved in a counter transfer direction may possibly press the paper sheet 2 at the uppermost position of the paper feed tray 1. If such a phenomenon occurs, the position of the uppermost print sheet 2 on the paper feed tray 1 is disordered by the pressurization and the stability of the next primary paper feed is thereby hampered. If the print sheet 2 is a flexible, hard sheet (e.g., a postcard or a cardboard), in particular, the returning force of the bent print sheet 2 for returning to a linear state is strong and the probability that the position of the uppermost print sheet 2 on the paper feed tray 1 is disordered becomes higher.
To cope with the above-stated situation, the inventors of the present invention gave a consideration to a paper feed unit A2 shown in FIGS. 8 and 9.
As shown in FIGS. 8 and 9, the paper feed unit A2 is constituted such that a one-way clutch 11 is attached to the rotary shaft 6 of a pickup roller 4 compared with the paper feed unit A1 shown in FIG. 7.
The one-way clutch 11 is supported by a side plate 12 which is provided on a paper feed unit main body side to prevent the rotation of the clutch 11. The one-way clutch 11 allows the rotation of the rotary shaft 6 of the pickup roller 4 when the rotary shaft 6 rotates in a paper feed rotation direction a. The one-way clutch 11 is locked to the rotary shaft 6 when the rotary shaft 6 thereof rotates in a paper feed counterrotating direction b and applied with a counterrotating force on the side plate 12, thereby preventing the rotation of the rotary shaft 6.
In FIG. 9, a reference numeral 13 denotes a scraper support member supporting the scraper roller 3. The scraper support member 13 is rotatably supported by the rotary shaft 6 and constituted so as not to rotate when the rotary shaft 6 rotates.
That is to say, in the paper feed unit A2 stated above, if primary paper feed is completed in a state in which the print sheet 2 is being bent, a pressing force in the counterrotating direction acts on the pickup roller by the returning force of the bent print sheet 2 for returning to a linear state. However, since the counter rotation of this pickup roller 4 is stopped by the one-way clutch 11, it is possible to suppress the rear end of the primarily fed print sheet 2 from pressing the uppermost print sheet on the paper feed tray 1.
In case of the above-stated paper feed unit A2, however, the primarily fed print sheet 2 cannot be transferred in counter direction. Due to this, if the jamming of the primarily fed print sheet 2 occurs, the print sheet 2 which has caused jamming cannot be pulled out from a paper feed tray 1 side. In other words, with the constitution of the paper feed unit A2, it is difficult to eliminate the print sheet 2 which has causes jamming.
The present invention has been achieved with the above-stated studies. It is, therefore, an object of the present invention to provide a paper feed unit capable of preventing the positions of sheets on a paper feed tray by a primarily fed sheet and also easily removing the sheet which has caused jamming.
To obtain the above-stated object, a paper feed unit according to the present invention is provided with: a paper feed tray stacking sheets thereon; a primary paper feed roller; a secondary paper feed member provided downstream to the primary paper feed roller in a transferring direction of the sheets, wherein an uppermost sheet among the sheets stacked on the paper feed tray is transferred toward the secondary paper feed member by rotation of the primary paper feed roller, the sheet is further transferred while a tip end of the sheet contacts with the secondary paper feed member, and primary paper feed is then completed while the sheet is being bent; a counter rotation stop mechanism allowing the primary paper feed roller to rotate in a paper feed direction but preventing the primary paper feed roller from rotating in a counter direction to the paper feed direction; and a rotation stop release mechanism releasing a state in which the primary paper feed roller is prevented from rotating in the counter direction by the counter rotation stop mechanism.
Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.